Handlebars.js is an extension to the Mustache templating
language created by Chris Wanstrath.
Handlebars.js and Mustache are both logicless templating languages that
keep the view and the code separated like we all know they should be.

Installing Handlebars is easy. Simply download the package from the
official site and add it to your web pages
(you should usually use the most recent version).

Alternatively, if you prefer having the latest version of handlebars from
the 'master' branch, passing builds of the 'master' branch are automatically
published to S3. You may download the latest passing master build by grabbing
a handlebars-latest.js file from the builds page. When the
build is published, it is also available as a handlebars-gitSHA.js file on
the builds page if you need a version to refer to others.
handlebars-runtime.js builds are also available.

Note: The S3 builds page is provided as a convenience for the community,
but you should not use it for hosting Handlebars in production.

You can register helpers that Handlebars will use when evaluating your
template. Here's an example, which assumes that your objects have a URL
embedded in them, as well as the text for a link:

Handlebars.registerHelper('link_to',function(){

return"<a href='"+this.url +"'>"+this.body+"</a>";

});

var context ={ posts:[{url:"/hello-world", body:"Hello World!"}]};

var source ="<ul>{{#posts}}<li>{{{link_to}}}</li>{{/posts}}</ul>"

var template = Handlebars.compile(source);

template(context);

// Would render:

//

// <ul>

// <li><a href='/hello-world'>Hello World!</a></li>

// </ul>

Helpers take precedence over fields defined on the context. To access a field
that is masked by a helper, a path reference may be used. In the example above
a field named link_to on the context object would be referenced using:

Handlebars.js supports an extended expression syntax that we call paths.
Paths are made up of typical expressions and . characters. Expressions
allow you to not only display data from the current context, but to
display data from contexts that are descendants and ancestors of the
current context.

To display data from descendant contexts, use the . character. So, for
example, if your data were structured like:

var data ={"person":{"name":"Alan"}, company:{"name":"Rad, Inc."}};

You could display the person's name from the top-level context with the
following expression:

{{person.name}}

You can backtrack using ../. For example, if you've already traversed
into the person object you could still display the company's name with
an expression like {{../company.name}}, so:

Whenever the block helper is called it is given one or more parameters,
any arguments that are passed in the helper in the call and an options
object containing the fn function which executes the block's child.
The block's current context may be accessed through this.

Block helpers have the same syntax as mustache sections but should not be
confused with one another. Sections are akin to an implicit each or
with statement depending on the input data and helpers are explicit
pieces of code that are free to implement whatever behavior they like.
The mustache spec
defines the exact behavior of sections. In the case of name conflicts,
helpers are given priority.

You can register additional templates as partials, which will be used by
Handlebars when it encounters a partial ({{> partialName}}). Partials
can either be String templates or compiled template functions. Here's an
example:

If using the precompiler's normal mode, the resulting templates will be
stored to the Handlebars.templates object using the relative template
name sans the extension. These templates may be executed in the same
manner as templates.

If using the simple mode the precompiler will generate a single
javascript method. To execute this method it must be passed to the using
the Handlebars.template method and the resulting object may be as
normal.

In a rough performance test, precompiled Handlebars.js templates (in
the original version of Handlebars.js) rendered in about half the
time of Mustache templates. It would be a shame if it were any other
way, since they were precompiled, but the difference in architecture
does have some big performance advantages. Justin Marney, a.k.a.
gotascii, confirmed that with an
independent test. The
rewritten Handlebars (current version) is faster than the old version,
and we will have some benchmarks in the near future.

There's a Gemfile in the repo, so you can run bundle to install rake
if you've got bundler installed.

To build Handlebars.js from scratch, you'll want to run rake compile
in the root of the project. That will build Handlebars and output the
results to the dist/ folder. To run tests, run rake test or npm test. You can also run our set of benchmarks withrake bench`.

If you notice any problems, please report them to the GitHub issue tracker at
http://github.com/wycats/handlebars.js/issues.
Feel free to contact commondream or wycats through GitHub with any other
questions or feature requests. To submit changes fork the project and
send a pull request.